An Improved Noninvasive Method for Measurement of Cardiac Output and Evaluation of Left-Sided Cardiac Valve Incompetence

A time-saving method was devel oped to label red blood cells in vitro with ^99mTc while avoiding centrifuga tion. After tin incubation, extracellu lar tin was oxidized by sodium hypochlorite, and EDTA was added for stabilizing the complex prior to ^99mTc incubation. Labeling yields were 95%, and in vivo decay showed a high stability with a mean biologic half-life of eleven hours. The first-passage radionuclide technique for determination of car diac output using the above-men tioned tracer was evaluated by using the left ventricle as area-of-interest with individual background correc tion after complete mixing of the tracer. This technique showed a high level of agreement with invasive methods. By combining this method for measurement of the forward stroke volume with the multigated equilib rium principle for determination of the total left ventricular stroke vol ume using similar background cor rections, an exact evaluation of re gurgitation fractions was obtained. In patients with aortic and mitral valve disease the noninvasive radio nuclide technique gave similar but probably more accurate results as compared with contrast aortography and ventriculography. The radionu clide technique may be suitable for monitoring and selecting patients for surgical treatment.